Capable of outrunning sail and rowboats, the sei whale (Balaenoptera borealis) was protected from whaling by its remarkable speed – until the advent of motorised chasers. The sei has been recorded at 50 kilometres per hour in a sprint. One travelled 4,320 kilometres in 10 days, indicating an average speed of 16 kilometres per hour if it made the trip without a rest.
Medium sized for a baleen whale, at an average weight of 20–25 tonnes and a length of 15–18 metres, the sei is nevertheless the equivalent of four large elephants. It is lean and sleek, steely grey, and has a high dorsal fin. It is estimated to live for more than 50 years.
Sei whales use two feeding methods. With their mouths half open they skim the sea’s surface for prey, then swallow what has collected on their 300–400 baleen plates. Alternatively, they open their mouths wide, taking in a huge quantity of food and water, then expel the water to leave the food behind.
Around February and March sei whales migrate south to Antarctic feeding grounds, but do not venture near the pack ice, as blue or fin whales do. They return to warmer waters to calve, passing through the Pacific Ocean to the east of New Zealand between the mainland and the Chatham Islands. The International Whaling Commission, which monitors whale populations, has no estimate for sei whale numbers.
Sometimes described as the ‘tropical’ whale, Bryde’s whales (Balaenoptera edeni) prefer waters warmer than 20°C, which are generally found in northern New Zealand.
The correct pronunciation of Bryde’s is ‘brewdus’. This whale is named after Johan Bryde, the Norwegian consul to South Africa, who built the first whaling stations in Durban.
It is the most common of the baleen whales around the New Zealand coast, and is seen mainly in springtime in the Bay of Plenty, Hauraki Gulf and off the east coast of Northland. Whether it migrates long distances is uncertain. Some experts believe Bryde’s whales, seen off the coast, mate and calve locally.
Appearance and diet
From a distance the Bryde’s whale is often confused with the sei: they are both sleek and grey, with a pointed dorsal fin. The Bryde’s is the second smallest of New Zealand’s baleen whales (the minke being the smallest), with an average weight between 16 and 20 tonnes and a length of 12–15 metres. Unlike many other baleen whales, which eat krill in polar waters, the Bryde’s feeds on fish, such as pilchards, mackerel and mullet.
The Bryde’s has been spared large-scale whaling. Up until 1962, New Zealand whalers working at the Whangaparapara station on Great Barrier Island hunted Bryde’s whales, although only 17 were ever taken. Out of an estimated original population of 60,000, there may be 40,000 left.
The minke whale is now believed to consist of two species:
- The common or northern minke whale (Balaenoptera acutorostrata), which in its large form is confined to the northern hemisphere. However, a sub-species, the dwarf minke, is found in New Zealand.
- The Antarctic or southern minke whale (Balaenoptera bonaerensis), which is confined to the southern hemisphere including New Zealand.
In New Zealand minke whales are not commonly seen, although of all the baleen whales they are the most likely to become stranded on the coast.
Appearance and diet
The dwarf minke, which is most often seen, is about 7 metres long, while the southern is about 9 metres long. The minke is also called the ‘piked whale’ or ‘sharp-headed finner’, because of its sharply pointed head. It is chunkier than its relatives and has a dark grey back with variable whitish markings. Sometimes there is a distinctive white band on the flipper.
Like the blue whale, the minke favours cold waters close to the Antarctic ice where it feeds on krill, but around New Zealand it relies more on fish and squid.
Whalers did not bother with minkes until the latter half of the 20th century, when the larger whale species had been hunted out. Since 1987 the Japanese have been killing more than 300 minkes a year, in defiance of world opinion, for purposes they define as scientific research.
There is debate about the size of the world’s minke population, but it is likely to be between 500,000 and 1,000,000.